1. Field of the Invention
The present invention relates to crystalline phosphor (fluorescent body) having a columnar shape, manufacturing method thereof and a light emitting device using the phosphor.
2. Description of the Background Art
Recently, phosphors using semiconductor crystals as matrix have been vigorously studied. Particularly, nano-size particle phosphors having luminous efficiency enhanced by quantum size effect have been much developed. Particularly, practical application of ZnS and CdSe, which are II-VI group compound semiconductors, as phosphor materials have been steadily studied, as these materials can be synthesized at a room temperature and nano-particles of uniform size can be synthesized in large amount by coprecipitation, reversed micelle method or the like, as described in ISOBE Tetsuhiko, “High Efficiency of Luminescence on Nanosized Phosphors” Applied Physics, Vol. 70, No. 9, pp. 1087-1091 (2001).
Nano-particle phosphors, however, tend to aggregate, and when specific surface area increases, luminescent killers derived from surface defects increase, degrading light emitting characteristic. In view of this problem, Japanese Patent Laying-Open No. 2003-226521 discloses a technique in which the surface of nano-particles is modified by a surface stabilizer, to attain the effect of defect capping and mono-dispersity.
On the other hand, nitride semiconductors such as GaN, InN and AlN, which are III-V group compound semiconductors, have superior light emitting characteristic and have been known as materials of light emitting device emitting blue-violet light of high luminance. A technique for manufacturing a phosphor using the nitride semiconductor as such has been proposed recently, as disclosed in Japanese Patent Laying-Open Nos. 2000-008035, 2003-034510 and 2003-063810.
The nitride semiconductor, however, is a chemically stable compound, and therefore, synthesis thereof requires high reaction temperature. Synthesis by reversed micelle method disclosed in ISOBE reference above or surface modification using a stabilizer disclosed in Japanese Patent Laying-Open No. 2003-226521 cannot be applied, as these methods employ materials that are much susceptible to pyrolysis.
By the methods disclosed in Japanese Patent Laying-Open Nos. 2000-008035, 2003-034510 and 2003-063810, it is impossible to obtain phosphor particles that can attain quantum size effect (specifically, particles smaller than twice Bohr radius). Particularly, in a method of obtaining phosphor particles by hetero-epitaxial growth of semiconductor around nuclear particles, crystal tends to grow in a specific orientation, and therefore, uniformly coated phosphor particles unavoidably come to have large diameter. Physical grinding of particles or surface modification by post processing can not remarkably improve luminous efficiency, while manufacturing process is troublesome and costly.
As described above, conventional nitride phosphors and manufacturing methods thereof cannot efficiently provide nano-particle phosphors having superior luminous efficiency.
The present invention was made in view of the conventional technical problems described above, and its object is to provide a phosphor having superior light emitting characteristic using nitride semiconductor material, a manufacturing method that can produce the phosphor with high production yield, and a light emitting device using the same.